tire selection changing the gear ratio

tire selection changes the gear ratio?

I've been digging through threads trying answer my question but ended up having more questions.
Like I've said, I've never had a "street truck". I would just get the biggest most aggressive tires I could afford for my trucks and go play in the mud.

I've got the 3.55 gears, I was wanting to go with a lower profile tire but after searching through threads I'm now concerned about messing up the gear ratio. It has the original tires on it now and I want to stay with the factory dipped rims.
So I reckon my Q is what tire size would y'all recomend that wouldn't affect the spoedo and gear ratio. I don't have a tuner to make adjustments to the system and I've read the dealer can only flash factory recommended sizes. Would a smaller tire have positive or negative affects as far gear ratio and performance?
Mainly I'm just wanting more/better all around traction.

Smaller diameter tires = higher numerically gear ratio.

This link has a gear ratio calculator. It's on the left of the page under "tire size help"

https://tiresize.com/chart/

Well that didn't help lol. There were duplicate tire sizes with different specs for the same size tire. I thought I had it figured out till I noticed that.
Maybe I drug that Q out a little too long? Idk, I'll figure out something.

I work on a lot of older cars, that now have relatively newer tires, and I just learned to deal with it. It's a pain, but depending on your commute, you can usually do the math. I remember putting larger skins on an old hot rod of mine, and asking a friend who had a new car to go out with me to gauge how fast I was really going. I called him on my cell while we driving, and my speedo said 60 mph. He said we were going 72. This is not nearly as disturbing as when my speedometer says 120, but you get the point.